Formaldehyde polymerization process and apparatus



Jan. 21, 1969 F. FOURNEL 1 3,423,363

FORMALDEHYDE POLMERIZATION PROCESS AND APPARATUS Filed Dec. 9, 1964 Sheet of (5 INVENTOR. FRANCIS FOURNEL.

BY @aqM Jan. 21, 1969 F. FQURNEL 3,423,363

FORMALDEHYDE POLMERIZATION PROCESS AND APPARATUS Filed Dec. 9, 1964 Sheet 2 4 of 5 INHJNTQR, FRANCIS FOURNEL AT 7' DA A 1 8 Jan. 21, 1969 F. FOURNEL 3,423,353

FORMALDEHYDE POLMERIZATION PROCESS AND APPARATUS Filed Dec. 9, 1964 Sheet 3 or 5 INVENTOR. s3 FRANCIS FOURNEL MFA 57s United States Patent Office 3,423,363 FORMALDEHYDE POLYMERIZATION PROCESS AND APPARATUS Francis Fournel, Paris, France, assignor to Produits Chimiques Pechiney Saint-Gobain, Paris, France Filed Dec. 9, 1964, Ser. No. 417,081 Claims priority, application France, Dec. 13, 1963,

957,164/ 63 US. Cl. 26067 Int. Cl. C08g l/OZ, 35/00 8 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a process of polymerization or copolymerization of compositions of formaldehyde as well as to apparatus for carrying out the process.

In accordance with the present invention a concentrated gaseous phase monomer of formaldehyde and a polymerization catalyst therefor, are brought simultaneously in contact with the surface of a reaction bed composed of dry granular polyforrnaldehyde in a reaction chamber. The reaction is exothermic and the reaction bed is maintained at a temperature favorable to the reaction by continuously withdrawing some of the polyformaldehyde from the bed, cooling the withdrawal material and returning a like amount of previously withdrawn and cooled material to the bed. In addition the bed is mixed constantly in order to continuously expose a fresh reaction surface to the monomer and catalyst and distribute cooled polyformaldehyde uniformly through the bed.

The apparatus for carrying out this process in accordance with the invention includes a rotary reaction chamber containing several balls or having vanes secured to the inner walls which tumble and mix the reaction bed as the chamber rotates. Inlets are provided for introducing the gaseous formaldehyde monomer and polymerization catalyst simultaneously into the chamber and a suitable outlet is provided for removal of the polymerized formaldehyde. The reaction bed is maintained at a temperature favorable to the polymerization by withdrawing metered amounts of the reaction bed from the chamber through a revolving valve, cooling the withdrawn material and returning cooled material to the bed through another revolving valve. The two revolving valves are arranged and operated to return to the bed an amount of cooled material equal to the amount being withdrawn so as to maintain the volume and level of the bed constant.

The reaction bed must be dry for the polymerization and the conveyor system may include means for drying the material of the reaction bed preparatory to the polymerization operation.

It is a principal object of the present invention to provide a process and apparatus for continuously polymeriziug or copolymerizing a gaseous composition of formaldehyde by bringing a stream of the composition and a polymerization catalyst therefor simultaneously into contact with the surface of a reaction bed in a reaction chamber in which the conditions of temperature and pressure and the freshness of the reaction surface are maintained constantly favorable to the polymerization.

3,423,363 Patented Jan. 21, 1969 A further object is to provide apparatus of the abovementioned type in which the reaction bed is maintained at a temperature favorable to the polymerization by continually withdrawing some of the material from the bed, cooling the withdrawn material and returning cooled material to the bed.

An additional object is to provide apparatus of the type described in which some material from'the reaction bed is continually being withdrawn from the reaction chamber, circulated through conduits outside the reaction chamber and subsequently returned to the bed in the chamber and in which heat exchange means associated with the conduits may be utilized to dry the material of the bed preparatory to the commencement of polymerization and then, when polymerization is commenced, to continuously cool and remove moisture from material taken from the bed and circulated through the outside conduits.

Another object is to provide apparatus of the type described in which the reaction bed is tumbled constantly as means to continually mix and thereby refresh the surface of the reaction bed.

A still further object is to provide apparatus of the type described in which the reaction chamber is a rotary chamber having means therein to thoroughly mix and tumble the material of the reaction bed as chamber rotates.

Further objects and advantages of the process and apparatus of the present invention will be apparent from the following detailed description and accompanying drawings in which:

FIG. I is a schematic diagram of apparatus in accordance with the invention in which material withdrawn from the reaction bed to be cooled and returned is transported by suspending it in an inert gas in a pneumatic conveyor system and is cooled by circulating the suspended material through a heat exchanger;

FIG. 2 is a schematic diagram of apparatus in accordance with the invention in which material withdrawn from the reaction bed for cooling is transported in an inert gas in a pneumatic system as in the apparatus of FIG. 1, but in which the cooling is accomplished by cooling the inert gas before the withdrawn material is suspended therein.

FIG. 3 is a schematic diagram of apparatus in accordance with the invention in which material withdrawn from the reaction bed to be cooled is transported by being suspended in an inert gas in a pneumatic conveyor system as in the apparatus of FIGS. 1 and 2 but in which the cooling is accomplished by periodically holding the material in a fluidized bed having a heat exchanger therein;

FIG. 4 is a schematic diagram of apparatus in accordance with the invention in which the material withdrawn from the reaction bed for cooling is transported by mechanical screw conveyors; in which the cooling is accomplished by circulating a cooling fluid through jackets around portions of the conveyor system; and in which, in addition, moisture may be removed from the material during operation of the apparatus by circulating a heated fluid through one of the jackets; and

FIG. 5 is a schematic diagram of apparatus in accordance with the invention in which the material withdrawn from the reaction bed for cooling is cooled by being shaken through a vibrating chamber which has a cooling jacket around it.

In accordance with the process of the present invention streams of a gaseous phase monomer of formaldehyde and a polymerization catalyst therefor are simultaneously brought in contact with the surface of a raction bed of polyformaldehyde in a reaction chamber. The polymerization catalyst is suitably an amine, such as triethylamine,

5 atoms of carb trogen associated with I n Th 1 t cast bed f P ymerizatio 1S OllllnuOuSl g is s it icli to flow into the reaction ch zinilitii n 8 1n n vrdes for a good cc in t ig u or lenewed and theieby P art 1 U1 a y in the form of a Powd (1 e fi a tream 10 normal has Sc 0115 ate f eaction. The chamber P 1c es), a vapor or an aelOsoL nely (llVlCled (not shown) secur til t bans therein or has Curved vines The polyformaldehyde of the reac of fine granules a d d mixing ction. 0 its Inner Walls to enhance the I] IS ry In th fi ture 6 V6 ples of trated i h appaiams of ih The 01 n i e rawin s and P yrn hzation reaction occurs as the mber 10 and the 1 descnbedharem the reaction catalyst come in contact with the surf i omer and the exception of the ege i dassocmted therewith with Ice 0 In an l d i he reaction chamber and the rea ction is foir i fr hi? 10 e lb t iii the liirawings 851mm giiyiiiieiiasgsisgsoitgrsigiiqal;

n or er to have the reaction continu men s in eac of the five figures.

ous as n and catalyst flow into the mber the tempgr zltfi rz ig t g Irlr the apparatus illustrated in FIG. 1 the system for chamber is maintained at a level favorable to the rea t' coo mg drying material f-rom the reaction bed is a (below 110 C and ei b\ b Y B c ion pneumatic conveyor system in which the material with- Pl era y etween 30 and 80 C.) 15 drawn from the bed 15 by operation of the revolving valve tion bed is in the form Containing less th ah m 015 e 1nvent1on illusand the reaction bed is. agitated or mixed constantiy so that 21 a. the bottom oi the hopper 19 is carried in a stream oi the surface of the reaction bed is continuously being rean inert carrier as, such as nitrogen, through a cooler 22 freshed. and a drier 23. The outlet of the valve 21 opens into a The reaction chamber is maintained at a favorable temconduit 24 which is between a blower 25 and the cooler 22 perature by continuously withdrawing metered amounts of and a stream of gas driven through the conduit 24 by the the polyformaldehyde from the reaction bed, cooling the blower 25 picks up the granular reactor bed material withdrawn material and at the same time returning similar passed into the conduit 24 by the valve 21 and carries it amounts of cooled material to the bed so that the bed through the cooler 22. The cooler 22 is a heat exchanger remains at approximately the same level. The volume of having an inlet 26 and an outlet 27 for circulation of a the reaction bed is about of the volume of the reac- 25 coolant, such as cold brine, through the exchanger. From tion chamber and the quantity of material Withdrawn from the cooler 22 the bed material flows through a conduit 28 the bed, cooled and returned to the bed in a given time is to the drier 23 which is a heat exchanger having an inlet generally between 20 and 500, and prefer-ably between 50 29 and an outlet 30 for the circulation of steam thereand 200, times the weight of new polymer produced o the through. After passing through the drier 23 the bed matebed in the same time. The exact rate at which the material 30 rial is carried by the gas stream through a conduit 31 to a from the reaction bed is circulated through the cooling cyclone separator 32 which separates the bed material cycle depends however upon the nature of the polymer or from the carrier gas. The carrier gas fiOWS out the top of copolymer being produced and the characteristics of the the cyclone separator through a conduit 33 back to the cooling circuit. blower 25 and the bed material drops into the hopper 17.

The reaction bed is constantly agitated by rotating the 35 The material which collects in the hopper 17 is then rereaction chamber about its longitudinal axis and by proturn d to the reaction bed 15 by the operation of revolving viding several balls in the chamber or vanes secured to the valv 18 and input conveyor 16. The revolving valve 18 is walls of the chamber so that the bed is thoroughly mixed p e in time with t e revolving valve 21 so that the by a tumbling action as the chamber rotates, amount of material returned to the bed 15 approximately Th polymerization process i accordance i h hi inequals the amount removed whereby the volume and survention is normally carried out at approximately at face level of the bed 15 remain substantially constant. pheric pressure, but it is possible to carry it out at presin p i n the d i 23 i nly used to prepare the bed sures above and below atmospheric. It is, however, highly 15 y drying it before the Polymerization is Commenceddesirable to avoid using formaldehyde monomers which For dry the bed the C r 10 is rotated and the reare in, or return to, a liquid state at the working temperavplving valves 21 and 18 and blower 25 are Operated to ture and pressure in the reaction chamber since this causes circulate material from the bed 15 through h C ng an arcacticn hi h i diffi ultto contI'QL drying system. Steam is circulated through the drier 23, Looking now at the drawings, apparatus i accordance but the flow of coolant to the cooler 22 is shut off and no with the invention comprises a rotary reaction chamber 10 monomer and Catalyst a d o the Chamber. Then when mounted for rotation about its longitudinal axis on supthe bed is Suiiiciehiiy y (1655 than 095% moisture) the porting and d i i ll 11 hi h engage annu1ar ib stream to the drier 23 is shut off, the coolant to the cooler 12 around the chamber 10. At one end of the chamber 10 22 is turned on and the how of monomer and eaiaiyst are inlets 13 and 14 for conducting respectively a stream gh t inlet tubes 13 and 14 to the chamber is of a gaseous phase monomer of formaldehyde and a Startedstream of a polymerization catalyst therefor simultane- The Operation of apparatus of 1 i5 iiibsiraied y ously into the chamber where they come in contact with a the following examples:

bed 15 of granular polyformaldehyde therein.

At this same end of the chamber 10 is a screw type EXAMPLE Ia input Conveyor 16 below a pp 17 With a i y Vaive The apparatus included a stainless steel rotary chamber 18 etw n t bottom of the pp and the input C011 having a capacity of 800 liters and having six curved Veyor y which pbiyiol'maidehyde is i'eiunwd to the bed vanes on its interior walls to assist the thorough mixing 17 aft r it has been eboied y a cooling and drying System of the reaction bed 15 as the chamber rotated. The whichis subsequently described in de volume of the hopper 19 was about 200 liters.

At its other end, the rc Chamber 10 Opens into a The reaction bed 15 filled about one-half the chamber hopper 19 which has an outlet 20 in the side and a revolv- 10 and consisted of a polymer of formaldehyde in mg villi/6.21 m the bottom As indicated the Ramon bed granular form and dried to contain less than 0.05% mois- 15 occupies about 30% of the volume of the chamber 10 mm b and extends through the opening m the end of the cham er The chamber 10 was rotated 16 revolutions per minute 10 into the hopper 19 with the top of the bed 15 about d h level with the outlet 20 from the hopper so that new polyan t a temperature ihe Chamber 10 was maintained mer produced on the top of the reaction bed 15 flows out at between and 5 C. by withdrawin material from through the outlet 20 the bed 15 through the revolving valve 21, cooling the In the operation of the apparatus the rotation of the Withdrawn maiehai i0 (measurefii in pp rotary reaction chamber 10 continually mixes the granular and lng oled mat rial to the bed at a rate of material of the reaction bed 15 so that the surface of the 600 kilograms per hour.

The material from the bed was carried through the cooling systems 'by a stream of nitrogen circulated by the blower 25 at 500 cubic meters per hour. The cooler 11 was a stainless steel heat exchanger having an eflective heat transfer surface of 1.2 square meters and brine at a temperature of 15 C. was circulated through it at 2.5 cubic meters per hour.

The pressure within the chamber was slightly more than atmospheric.

A monomer consisting of dry gaseous formaldehyde was introduced into the chamber at a rate of 8 kilograms per hour simultaneously with a polymerization catalyst which was triethylamine introduced at a rate of 100 milligrams per hour carried in a stream of nitrogen flowing at a rate of 50 liters per hour.

The gases thus introduced contained more than 99.5% of the formaldehyde monomer by weight.

This produced 7.6 kilograms per hour of new polymer of formaldehyde from the outlet 20. The average yield of the polymerization process was therefore about 95%.

EXAMPLE Ib In the same apparatus used for Example la the monomer introduced into the chamber 10 was of a dry formaldehyde gas mixed with about 1% of furfuraldehyde which was prepared by bubbling pure formaldehyde through a flask containing furfuraldehyde which was maintained at a temperature of 80 C. This mixture was introduced at a rate of 8 kilograms per hour.

The polymerization catalyst was a mixture of alpha and beta picolines introduced at a rate of 1.6 grams per hour diluted in a stream of nitrogen flowing at 50 liters per hour.

The temperature in the reaction chamber 10 was maintained between 50 and 55 C. and the material from the reaction bed was circulated through the cooling system at a rate of about 600 kilograms per hour and was cooled to about 38 C. as measured in the hopper 17.

The new polymer contained about 1% furfuraldehyde (measured spectrographically) and the yield was nearly equal to the amount of monomer introduced.

In the apparatus illustrated in FIG. 2 the cooling system is a pneumatic system and material withdrawn from the reaction bed 15 through the revolving valve 21 is cooled by previously cooling the inert gas (e.g. nitrogen) in which the bed material is carried. For this purpose a stream of inert carrier gas is forced by blower 25 through a conduit 35 to a cooler 36 which is a heat exchanger having an inlet 37 and an outlet 38 for circulation of a coolant, such as cold brine, therethrough.

From the cooler 36 the cooled carrier gas flows through a conduit 39 which connects with the outlet of revolving valve 21 so that the bed material withdrawn through the valve 21 is picked up by the cooled carrier gas flowing in the conduit. From the valve 21 a conduit 40 conducts the carrier gas and its load of bed material to the cyclone separator from which the gas flows through a conduit 41 back to the blower 25 and the bed material drops down with hopper 17 from which it is returned to the reaction bed 15.

The operation of the apparatus of FIG. 2 is illustrated by the following examples:

EXAMPLE Ila The reaction chamber 10 was a stainless steel drum of 800 liters capacity, having vanes therein and rotated 16 revolutions per minute as in Examples Ia and 1b.

The reaction bed 15 filled about one-half the chamber 10 and was made up of polyformaldehyde powder containing less than 0.05% moisture. It was circulated through the cooling system at about 600 kilograms per hour in nitrogen circulated by the blower 25 at about 600 cubic meters per hour.

The nitrogen carrier gas was cooled in a cooler 36 having 1.5 square meters of heat transfer surface cooled by brine at l5 C. circulated through the cooler at a rate of about 2.5 cubic meters per hour.

This system cooled the bed material circulated in the cooling system at 40 C., as measured in hopper 17, so that the temperature of the reaction bed 15 in the chamber 10 was maintained between 50 and C. The pressure was slightly above atmospheric.

Monomer consisting of pure dry formaldehyde gas was fed into the chamber 10 at 8 kilograms per hour. The catalyst which was hexatrimethylaminosilane diluted in a stream of 50 liters per hour of nitrogen was fed simultaneously into the chamber at a rate of 0.8 gram per hour.

New polymer was produced at a rate of about 8 kilograms per hour. The yield was therefore about equal to the monomer processed.

EXAMPLE IIb The same apparatus and operating conditions as in Example IIa were used except that the catalyst was pyridine fed into the chamber at 2.5 grams per hour.

The results were the same as in Example IIa. That is, the yield of new polymer about equaled the monomer introduced.

Looking now at FIG. 3, the apparatus of the invention illustrated has a cooling system in which the cooling is accomplished in a fluidized bed 43 having cooling coils 44 therein.

The fluidized bed 43 is formed in a chamber 45 with the powdered polymeric material of the reaction bed 15 which flows into the chamber 45 through the revolving valve 21. The material is fluidized by a stream of inert gas, such as nitrogen, circulated by the blower 25 through a conduit 46 to the bottom of the chamber 45 where it flows up through a screen 47 and through the bed material on the screen.

At the top of the chamber 45 is a cylindrical stack portion 45a having a filter 48 therein. A movable cap or valve 49 is arranged in the chamber 45 to close or open the stack portion 45a to the main part of the chamber in which the fluidized bed 43 is situated. A conduit 50 from the top of the chamber 45 connects the stack portion 45a into a conduit 51 which goes to the,cyclone separator 32. From the cyclone separator gas is returned to the blower 25 through a conduit 52. The main part of the chamber 45 is also connected into the conduit 51 through a conduit 53 having a valve 54 therein and opening into the chamber 45 at a point below the stack portion 45:: and valve 49.

For cooling the material withdrawn from the reaction bed 15 through the revolving valve 21, the valve 54 is closed and the valve 49 to stack portion 45a is opened. Material through the revolving valve 21 drops down into the main part of the chamber 45 where it is fluidized by the gas circulating up through the screen 47. The gas flows through the fluidized bed 43 through the stack portion 451: and through the conduits 50, 51 and 52 back to the blower 25. Any material carried up from the fluidized bed 43 is trapped by the filter 48 and falls back into the bed 43.

The material in the fluidized bed 43 is cooled by a coolant, such as cold brine, circulated through the cooling coils 44 in the bed. When the material has been cooled to the desired temperature, the valve 49 is closed and valve 54 is opened. The cooled material from the fluidized bed is then carried by the stream of gas out of the chamber 45 through conduits 53 and 51 to the cyclone separator 32 from which the cooled bed material drops into the hopper 17 to be returned by the input conveyor 16 to the reaction bed 15.

For the apparatus illustrated in FIG. 4 material withdrawn from the reaction bed 15 through the revolving valve 21 is carried by mechanical screw conveyors 55, 56, and 57 in a circuit back to the hopper 17. Cooling is accomplished by cooling jackets 58 and 59 respectively around the conveyors 55 and 56 through which a coolant, such as cold brine, is circulated. Both of the cooling jackets 58 and 59 may be used for cooling or one of them may be used as a heater by circulating steam through it as a means to remove small amounts of moisture which have been absorbed by the bed material during the process.

In the apparatus shown in FIG. bed material withdrawn through the revolving valve 21 for cooling drops onto a vibrating screen 60 in a chamber 61 which has a flexible inlet 62 and a flexible outlet 63 in order to permit the chamber 61 to be vibrated. Any particles of the bed material which do not pass through the screen 60 are withdrawn from the chamber 61 through an outlet 64.

The bed material is cooled by a cooling jacket 65 around the chamber 61 by circulating a coolant, such as cold brine, through the jacket. From the chamber 61 the cooled bed material is carried to the hopper 17 by a mechanical screw elevator 66 and from the hopper 17 the material is returned to the reaction bed by the inlet conveyor 16.

The process and apparatus in accordance with the invention as described above has the particular advantages of being simple and of producing uniformly high quality polymers at a good rate of continuous production.

The polymers and copolymers of formaldehyde produced by the process and with apparatus of the present invention are plastic resins which are useful for the production of molded or extruded articles or which may be drawn into fibers.

As many apparently widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments.

What is claimed is:

1. An apparatus for the polymerization of formaldehyde, comprising a polymerization chamber, means to inject concentrated gaseous monomers of formaldehyde, into said chamber, means for withdrawing granular polymer from the chamber and for maintaining a body of granular polymer within said chamber, said body occupying at least about of the volume of the chamber, means for feeding granules of polymer into the chamber, and means to maintain a selected temperature in the chamber comprising cooling means outside said chamber, and means for circulating granular polymer from the chamber through the cooling means and back to the chamber, said circulating means having a capacity to handle at least twenty times the weight of polymer as compared to the weight of monomer introduced, and means to mix the granular polymer in the chamber of the monomer.

2. An apparatus according to claim 1, in which the recycling circuit through the cooling means comprises pneumatic conveyor means and a separator for separating solids from gases.

3. A process for the continuous polymerization of a stream of gaseous monomeric formaldehyde, which comprises establishing a dry bed of granules of polyformaldehyde in a reaction chamber, injecting a stream of gaseous formaldehyde and a trace of catalyst into said chamber, moving the granules of said bed to contact the granules with the gaseous formaldehyde, maintaining the granules of the bed at a temperature favorable for the reaction polymerization of the formaldehyde composition at their surfaces to form desirable high molecular weight polymers, by removing a portion of said granules from the chamber, cooling the removed granules in a zone exteriorly of said reaction chamber to a temperature lower than that existing in any part of said reaction chamber, and reintroducing the cooled granules into the bed in said reaction chamber.

4. A process according to claim 3 which includes a composition of formaldehyde selected from the group consisting of monomeric formaldehyde and mixtures of monomeric formaldehyde and furfuraldehyde.

5. A process according to claim 4 in which the amount of granules removed from the bed exceeds the amount of granules returned to the bed b the amount of polymer produced and in which the amount of polymer granules returned to the bed is at least twenty times the amount of polymer produced.

6. A process according to claim 3 in which the volume of the reaction bed is from about 30% to about 50% of the volume of the reaction chamber.

7. A process according to claim 6 in which the quantity of the reaction bed withdrawn from the reaction bed, cooled and returned in a given time is within 200 to 500 times the quantity of new polymer produced upon the bed in the same time.

8. In the method according to claim 3 of continuously polymerizing formaldehyde in gaseous phase, by introducing simultaneously in a reaction chamber gaseous formaldehyde monomer and a catalyst in contact with a body of powdered polymer, the improvement which comprises establishing a body of powdered polymer in a rotary reaction chamber the volume of polymer being from about 30% to about 50% of the volume of the reaction chamber, the monomer being substantially pure, the thermal equilibrium of the reaction chamber being maintained by continuously withdrawing powdered polymer from said body, circulating it through an external cooling circuit and reintroducing it into the reactor, the quantity of the reaction bed withdrawn from the reactor, cooled and returned in a given time being within 20 to 500 times the quantity of new polymer produced in the same time.

References Cited UNITED STATES PATENTS 3,215,505 11/1965 Schmalfeld et al. 23288.3 XR 3,233,981 2/1966 Scott 23-2883 XR 3,285,877 1l/l966 Kocher et al. 260-67 2,951,059 8/1960 Axtell et al. 26067 2,982,758 5/ 1961 Michaud 26067 3,118,859 1/1964 Dclassus et al 26067 3,281,395 10/1966 Fukita et al 26067 3,296,205 1/1967 Kocher et al. 260-67 FOREIGN PATENTS 1,285,909 1/ 1962 France.

WILLIAM H. SHORT, Primary Examiner.

L. M. PHYNES, Assistant Examiner.

U.S. Cl. X.R. 23-288.3 

